Electroplating baths



Patented Mar. 6, 1945 I 2,370,986 ELECTROPLATING BATHS John S. Nachtman, Pittsburgh, Pa.

No Drawing. Application June 26, 1940,

Serial No. 342,525

6 Claims.

This invention relates to electro-plating baths.

and consists in additions made to such baths vwith the object and effect of obtaining deposits of superior quality. I shall first describe the invention in specific application to the tin-plating bath, and in the sequel shall indicate its wider and more general applicability.

, As is well known to those familiar with the characteristics of tin electro-deposition from acidic solutions, certain organic addition agents are requisite, in order to obtain from baths containing free acid fine-grained stannous deposits. Without such an addition agent the tin deposit is not sufficiently adherent to the base material; it tends to take the form of large needles of tin crystals with axes perpendicular to the surface of the base metal; and, usually, the base metal is not completely covered, but may be seen through spaces between the crystals. Much has been written and patented on various organic addition agents to be used with acidic tin baths. Among agents that have been proposed are protein-type colloids, such as gelatin or glue; cresols and sulfonated cresols; phenols and sulfonated phenols, such as phenol sulfonic acid; gums; starches, etc. After making a thorough investigation of the suggested baths found in the literature, and finding none that gave a truly satisfactory deposit for the subsequent melting of the tin deposit, especially on a steel base (with the exception of the electrolytic acidic tin bath described in my application Electrolytic Processes and baths" Serial No. 186,905), I proceeded in search of other adequate material.

As sulfonated organics containing the hydroxyl group seemed to have a salutary effect on the production of fine-grained tin deposits, I selected a newly marketed phenol and sulfonated it in the laboratory. This material was ortho-cyclohexylphenol. I sulfonated it with an equal weight of concentrated sulfuric acid (making repeated runs) at temperatures ranging from 80 1". to 200 F. and for periods of time ranging from minutes to 3 hours. Although under most all temperatures and times of sulfonation the water-soluble product obtained seemed, without other addition agent, to have a beneficial effect, the material obtained by sulfonating o-cyclohexylphenol with 10% (by weight) excess of sulfuric acid (that is, 10% more sulfuric acid than is required to form the mono-sulfonic acid of ocyclo-hexylphenol) at 130-140 F. for a period of .time ranging from 45 minutes to 1 hour proved to give the maximum beneficial effect in the acidic tin solution. For example, 20.6 g. orthocyclo-hexylphenol is sulfonated at 130-140" F. for 45 minutes to 1 hour with 12.65 g. sulfuric acid, giving approximately 30 g. of the .sulfonated material. The following is an example of a tin bath using this material:

Example 1 Grammes per litre Stannous sulfate 200 Hydrofluoric acid (100%) 97.4

01' Hydrofluoric acid (30%) 325) O-cyclo-hexylphenol sulfonic 4 acid or the sodium salt thereof 20-30 Such a solution gives a satisfactory deposit at -120 F. and at current densities of 10 to 300 amperes per square foot.

Example 2 Grammes per litre Stannous sulfate 200 Hydrofiuoric acid 30% 325 O-cyclo-hexylphenol sulfonic acid 20-30 Nicotine 1o Duponol 80" 33.6

The bath of the above example is operable under the same conditions of the bath of Example 1.

During my experimental work on the sulfonated phenol I found another phenolic compound, sold under the trade name of Bis-Phenol A (which is p-p'-isopropylidene bis-phenol) to be quite satisfactory as a tin-bath addition agent. This material was sulfonated with an equal weight of sulfuric acid at F. for 14 hours. Examples of baths using this material are as follows:

' Example 3 Y Grammes per litre Stannous sulfate 200 Hydrofluoric acid (30%) 325 Sulfonated p-p-isopropylidene bis-phenol- 10-30 ylphenol, or sulfonated The baths of Examples 3 and 4 will operate under the same conditions stated for Example 1.

sulfonated o-cyclo-hexylphenol and sulfonated p-p'-isopropylidene bis-phenol may be combined in the same bath, if desired.

The baths of the examples given (1-4) are operable, either with soluble anodes of tin, or with insoluble anodes, of such material as carbon, lead, etc.

It will be understood that I am not limiting myself in the use of the various ingredients to the concentrations given in Examples 1 to 4. The components may be varied through rather wide ranges of concentration, to meet the needs of cost, current density, and type of deposit desired. The operating conditions also may be varied, to meet the different ranges of composition. The salt of tin used may be stannous oxide or stannous fluoride or other stannous salt, and the hydrofluoric acid maybe replaced by sulfuric acid or other mineral or organic acids. Using the addition agents of Example 2 a sulfuric acid bath may be as follows:

Grammes per litre stannous sul 100 Hydrofluoric acid (30%) 325 Nicotine Duponol 80 33.6 sulfonated a-naphthol 10-30 The concentration of the various components of the bath of Example 5 may also be varied to meet desirements of operating conditions and cost of solution. v

The alkali salts, such as th sodium and potassium salts, of o-cyclo-hexylphenol and p-p'-isopropylidene bis-phenol sulfonic acids are also satisfactory for use, in place of the acids themselves.

In using these sulfonated phenol products, much smaller concentrations are required than is the case with the older baths described in the literature, such as sulfonated cresol or plain sulfonated phenol, a decided advantage from the cost standpoint.

I have described the use of nicotine as an addi tion agent, together with sulfonated o-cyclo-hexphenol, or both, for a tin-plating bath; and I have given a case (Example 6) in which, in association with nicotine and Duponol 80, sulfonated a-naphthol is effective.

I have found that equally with the sulfonated phenols already named, the sulfonated ortho p-p' -isopropylidene bistrine, etc. Nicotine, however, has never to my phenol salts are effective.

phenols generally and other specifically o-phenyl I have further discovered that, setting the sulfonated phenols aside, nicotine itself, alone or in association with Duponol as a wetting agent, is an eflective addition agent, affording improvement in the quality of the deposit, not to the tin-plating bath only, but to electro-plating baths generally, for the deposit of zinc, lead, tin, and the lead-tin alloy of terne-plate; and is serviceable in the plating of steel strip, sheet, and wire. Such use of nicotine I believe to be wholly new. As is the case in tin-plating, so in metal-plating generally, that addition agents are necessary, to obtain fine-grained, heavy deposits, free from trees" on the shar edges or projections. The literature abounds with suggestion of use of different addition agents in these baths, agents such as gelatin, glue, peptone, p-naphthol, cresol, sulfonated cresol, clove oil, gum arabic, tannic acid, dexknowledge been suggested in this connection.

My first use of nicotine was in a chloride zinc bath, and I found it to have very great effect in eliminating coarseness and treeing" of the deposit. This was particularly true in the making of heavier deposits, or the order of one half to two ounces to the square foot of surface area. Further work showed that the use of nicotine was beneficial in acidic tin baths, lead baths, and terne baths. In many cases I found it desirable to use nicotine in association with other addition agents such as a protein-type colloid, and, particularly, in association with such a wetting agent as Duponol *80.

The following are examples of baths in which nicotine proved its worth as a satisfactory addition agent:

Grammes per litre Zinc sulfate (7 H2O) 300 Ammonium chloride 50 Nicotine s 10 Ammonium thiocyanate 5 The baths of Examples 7 and 8 were operated at pH value of 2.5 to 3; the bath of Example 1 was operated at 50-300 amperes per square foot, while that of Example 2 at 25-150 amperes per square foot of surface; and both on steel strip, and at room temperature.

TmBArns Examples are given above.

LsAnBsms Example 9 Grammes per litre White lea Hydrofluoric acid (30%) 638 Boric acid 184 Nicotine 10 Alpha-naphthol I 2 those familiar with the art realize were operated Example Grammes per litre White lead 1 62.5 Perchloric acid (68%) 85 Peptone l Nicotine The baths of Examples 9 and l0'were operated at room temperature; the bath of Example 9 was run at -150 amperes per square foot, and that of Example 10 was run at l0-50 amperes per square foot.

The bath of Example 11 was operated at room temperature and at 25-150 amperes per square foot. I

In all of the examples given the metallic salts named may be substituted with other salts (organic or inorganic) of the same metals. The acidity of the bath may be varied over a rather wide range; the degree of concentration, both of the metallic salt and of the addition agent may be varied over a rather wide range; and the bath temperature may be varied-4111 to meet the various requirements of character of deposit, cost of solution, and current density. The baths are operable with either soluble or insoluble anodes,

and give dense, fine-grained deposits, suitable as coatings upon steel, or upon other conductors, metallic and non-metallic.

Nicotine I have found to be a very valuable addition agent, in replace the protein-type colloids, such as gelatin, glue, or peptone,vcommonly used in electrolytic baths; it has long operating life, and forms no gummy precipitate or sludue with the salts of the bath. If desired, nicotine may be used together with the protein-type colloid.

I have discovered a relationship between speed of travel of the strip through the plating bath (with corresponding increase in current density per square foot) and fineness of the deposit. Strip speed in the operation as it has heretofore been known has been at the rate of to 100 feet per minute. I have found that if I greatly increase speed, above 200 feet per minute, and, as I prefer, to approximately 1000 feet per minute:

' and if correspondingly I increase current density from the conventional 100 amperes per square foot of surface to 1000 or more amperes (with rapid circulation or agitation of the electrolyte between anode and cathode) I gain a deposit of notably finer grain structure and of harder quality and on such account of superior utility.

I claim as my invention:

1. An electroplating bath in which, in hydrofluroic acid solution, nicotine and sulfonated o-cyclo-hexylphenol are present with stannous sulfate.

2. A tin-plating bath; carrying a stannous salt in a solution of an acid selected from the group consisting of hydrofluoric and sulphuric acid, sulfonated o-cyclo-hexylphenoi and nicotine.

3. A tin-plating bath of substantially the following composition:

Grammes per litre Stannous sulfate 150 Sulfuric acid 22.5 sulfonated o-cyclo-hexylphenol 20-30 Nicotine 10 Sodium salt of the sulfate ester of a mixture of aliphatic alcohols in which the Cl chain length predominates 33.6

4. A tin-plating bath carrying a stannous salt in a solution of an acid selected from the group consisting of hydrofluoric and sulphuric acid, a sulfonated organic substance containing the hydroxyl group, chosen from the group that consists of o-cyclo-hexylphenol, o-phenyl phenol,

p-p'-isopropylidene bis-phenol and a-naphthol,

together with nicotine.

5. A tin-plating bath carrying a stannous salt in a solution of an acid selected from the group consisting of hydrofluoric and sulphuric acid, a sulfonated organic substance containing the trydroxyl group, chosen from a group that consists of o-cyclo-hexylphenol, p-p'-isopropylidene bisphenol, o-phenyl phenol, and a-naphthol, to-

sodium salt of the sulfate ester of a mixture of aliphatic alcohols in which the Cl chain-length predominates, together with nicotine.

, 6. A tin-plating bath of substantially the following composition:

Grammes per litre Stannous sulfate 200 Hydrofluoric acid (30%) 325 O-cyclo-hexylphenol sulphonic acid 20-30 Nicotine (95%) 10 Sodium salt of the sulfate ester of a mixture of aliphatic alcohols in which the 0, chain length predominates sac JOHN S. NACH'I'MAN. 

